As differs from four-stroke engines, two-stroke marine engines have the problem that the supply of oil for lubrication, and thus for reducing wear, must take place by way of oil injection systems. These systems must provide sufficient oil at a suitable time to ensure sufficient lubrication of the cylinder surface/piston rings. A common feature of all known systems is that the oil supply must be carried out under conditions of gas counterpressure. Considering that modern marine engines are operated with rotational speeds of approximately 100 rpm at strokes of up to 2500 mm, the unit of time for the oil distribution is very difficult to establish. In a piston/piston ring system measuring 900 mm in diameter and an oil supply system having approximately 8 intake ports distributed over the circumference, independent oil distribution develops in the circumferential direction by means of the installed components (piston rings) measuring approximately 350 mm,
This shows that a conventional piston ring design contributes no more than 3% to the distribution of the oil quantity due to the lack of pressure differentials on the circumference.
Oil supply systems were previously developed that were intended to ensure more rapid oil distribution during supply, despite high counterpressure. Complex piston/piston ring systems to support better oil distribution, which in reality would be difficult to implement, are unknown to date.
U.S. Pat. No. 6,536,385 B1 discloses a piston ring that is provided with geometrically different profiles on the running surface side. This piston ring can be used, in particular, for the oil lubrication of two-stroke engines. Piston rings that are disposed on top of each other and have convex running surfaces are used in a piston/piston ring system, wherein the piston ring is designed to be conical to receive a piston ring groove configured in corresponding fashion, at least in the region of the flank surface of the ring facing a combustion chamber.
DE 10 2006 058 081 A1 discloses a two-stroke internal combustion engine, comprising at least one port of a gas control system of an inlet and/or of an outlet, wherein a gap between a piston and a running surface surrounding the piston is sealed, wherein a combination seal for sealing the gap is provided in the running surface, the piston sliding along this combination seal in such a way that the combination seal has both a gas sealing function and an oil scraping function.
It is the object of the invention to create a piston/piston ring system, in which more uniform oil distribution over the entire running surface of the piston rings, as seen in the circumferential direction, is generated, wherein the absolute oil quantity is also to be reduced.